Traditionally, commercial power from a utility has been used as the primary source of electrical power for a consuming entity, e.g., a telecommunications facility. Many power systems include backup power sources to deliver power in the event the utility is unable to deliver power. Black-outs and other disturbances in the commercial power grid make this necessary. To accomplish this, many facilities use a diesel generator. The diesel generator is then backed up by an array of batteries.
Conventionally, all of these systems—the commercial AC receiving equipment, the diesel generator, and the batteries—are all physically installed around or in the facility. The installation process drains engineering time because it typically involves customizing the equipment to meet the needs of the facility.
Operationally, if power from the commercial utility is lost, the diesel generator is activated to supply power to the facility. It takes time for the diesel generator to come online, though. Because of this, the battery array provides power during the time it takes to switch from the utility source to the diesel-generated source. If the generator also fails (e.g., runs out of fuel), then the battery array is able to provide power for an additional (but limited) period of time.